Drill bit and method for preparing a bone for a fixation screw

ABSTRACT

A method of preparing a bone to receive a fixation screw through a fixation device includes providing a drill bit sized and configured to pass through a bore in a fixation device positioned in the bone and drilling a passage into the bone and through the bore. At least a distal portion of the drill bit passes through the bore in the drilling step. At least an outer portion of the distal portion of the drill bit has a hardness that is less than a hardness of the fixation nail.

BACKGROUND

Devices such as intramedullary rods, bone nails, bone screws, plates,etc. may be affixed to a bone to repair or strengthen fractured orotherwise damaged or diseased bones, often by fixing two or more bonesor bone pieces with respect to each other, in which case the device maybe referred to as a fixation device. Such fixation devices share theload with the bone to support the bone as it heals. The fixation devicemay be further adapted to deliver medication or other fluids into bone.

For unthreaded, smooth-sided devices, secondary fixation devices such asscrews may be used to rotationally fix the fixation device to the bone.These screws are generally oriented orthogonally with respect to thefixation device and pass through bores formed in the fixation device. Adrill is used to form a passage in the bone, the passage extendingthrough the bore in the fixation device. The drill bits used for suchprocedures are typically formed of a similar material to the fixationdevice itself, such as a stainless steel or titanium alloy or a materialthat is harder than the material from which the fixation device isformed.

If the drill is improperly oriented during the drilling procedure or ifthe drill bit is too large in diameter relative to the bore, the drillbit may contact a portion of the fixation device (e.g., the portion ofthe fixation device surrounding the bore) and cause scoring or otherphysical damage to the fixation device. Such physical damage cancompromise the effectiveness of the fixation device, such as byphysically weakening the fixation device in a high stress area or byaffecting the delivery of medication or other fluids to the bone.

SUMMARY

One embodiment of the invention relates to a method of preparing a boneto receive a fixation screw through a fixation device. The methodincludes providing a drill bit sized and configured to pass through abore in a fixation device positioned in the bone and drilling a passageinto the bone and through the bore. At least a distal portion of thedrill bit passes through the bore in the drilling step. At least anouter portion of the distal portion of the drill bit has a hardness thatis less than a hardness of the fixation nail.

Another embodiment of the invention relates to a bone fixation systemincluding a fixation device configured to be positioned at a target areaof bone and a drill bit. The fixation device includes two ends connectedby a shaft and includes a bore formed through the shaft configured toreceive a fixation screw. The drill bit is sized and configured to passthrough the bore to prepare the surrounding bone to receive a secondfixation device. At least a distal portion of the drill bit isconfigured to pass through the bore. The fixation device is made of afirst material and the distal portion of the drill bit comprises atleast an outer portion made of a second material. The second material ofthe drill bit has a hardness that is less than the hardness of the firstmaterial of the fixation device.

Another embodiment of the invention relates to a drill bit for preparinga hole in a bone. The drill bit includes a drill bit shaft having adistal portion sized and configured to be received through a bore in afixation device. The distal portion has a hardness of between thehardness of the bone and the hardness of the stainless steel, or lessthan the hardness of the stainless steel.

Alternative exemplary embodiments relate to other features andcombinations of features as may be generally recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, wherein like reference numerals refer to like elements.

FIG. 1 shows a fixation system including a fixation nail inserted intothe femur bone of a patient and secured by fixation screws, according toan exemplary embodiment.

FIG. 2 shows a perspective view of a bone screw insert being insertedinto the fixation nail of FIG. 1.

FIG. 3 shows a drill forming a passage for a fixation screw of thefixation system of FIG. 1.

FIG. 4 shows a side view of a drill bit for forming a passage for afixation screw of the fixation system of FIG. 1, according to anexemplary embodiment.

FIG. 5 shows a partial cross-section view of a drill bit for forming apassage for a fixation screw of the fixation system of FIG. 1, accordingto another exemplary embodiment.

FIG. 6 shows a side view of a drill bit for forming a passage for afixation screw of the fixation system of FIG. 1, according to anotherexemplary embodiment.

FIG. 7 shows a cross-section view of a drill bit for forming a passagefor a fixation screw of the fixation system of FIG. 1, according toanother exemplary embodiment.

FIG. 8 is a flowchart of a method of preparing a bone to receive afixation screw through a fixation device, according to an exemplaryembodiment.

DETAILED DESCRIPTION

Referring generally to the figures, a cannulated fixation nail (e.g.,bone nail, intramedullary nail, intramedullary rod, intramedullary pin,etc.) is configured to stabilize a bone or multiple bones by holding twoor more bones or bone pieces in a fixed spatial relationship withrespect to each other. The bone nail may be coupled to the exteriorsurface of the bone or may be disposed in an interior portion (e.g., themedullary canal) of the bone. The bone nail may be secured with one ormore fixation devices, such as bone screws that engage both the bonenail and the surrounding bone tissue. The bone nail and/or the bonescrew may be cannulated and used to deliver desired substances to thevicinity of a bone. In certain embodiments, the nail and/or the screwsmay also be fenestrated or permeable to the substance to be delivered.The substances to be delivered may include medicants or therapeutics, orother substances which are desirable to deliver to the vicinity of abone. The substance or a combination of substances may be delivered tothe interior of a bone, to the exterior of a bone, to the fractureinterface between two or more broken bones, or to any other location.

A nail or screw may be “cannulated” in that it includes a hollow cavitydisposed inside at least part of its shaft. For example, the cavity mayconsist of a bore beginning at or near one end of the nail or screw andextending longitudinally into the nail or screw. Other configurationsare possible, however, and the hollow cavity need not be restricted to acylindrical shape or a circular cross-section. The cavity may extendthroughout the entire length of the nail or screw, thus creatingopenings at each end of the nail or screw, or alternatively, the cavitymay extend only partially into the interior of the nail or screw. Theshape and size of the cavity may be suitably chosen to allow delivery ofthe desired substance through the nail or screw to the bone area ofinterest. When it is desired to use the cannulated portion of the nailor screw as reservoir for the substance to be delivered, for example,the cavity may be made as large as possible so long as the screw andinsert maintain the structural integrity needed for introduction intothe bone.

As used herein, the term “bone screw” is intended to refer to screws ofall types which are presently known or hereafter devised forimplantation into bone. In this regard, cancellous screws, corticalscrews, and machine screws are all contemplated as being within thescope of bone screws. Bone screws typically include threads along atleast a portion of the exterior of the screw shaft, but it should beappreciated that tacks, pins, nails and the like may also be includedwithin the definition of a bone screw, whether threaded or unthreaded.When threads are present, it may be found advantageous to useself-tapping threads, or alternatively, the threads can be pre-cut inthe bone prior to bone screw insertion.

Referring to FIGS. 1-3, a fixation system includes a fixation device,shown as a fixation nail 100 disposed within a bone 102. As shown inFIG. 1 according to one embodiment, the fixation nail 100 is disposed inthe intramedullary cavity of the femur. In other embodiments, thefixation system may be utilized to stabilize any other suitable bone,such as a humerus, tibia, etc. The fixation nail 100 may be disposed inthe interior of the bone 102 or may be disposed along the exteriorsurface of the bone 102.

The fixation nail 100 has two ends 104 and 106 connected by a shaft 108.All or a portion of the shaft 108 may be cannulated. The shaft 108 ofthe fixation nail 100 may include fixation nail fenestrations 110,through which a substance may pass from the cannulated shaft 108 to thesurrounding bone tissue. The substance provided to the bone may be, forexample, medicants or therapeutics, or other substances which aredesirable to deliver to the vicinity of a bone. One end of the fixationnail 100 may be configured to accept a nail insert 114. This isdemonstrated in FIG. 2 which shows a perspective view of the fixationnail 100 having internal threads 112 on one end 104 to promote fixationof the nail insert 114 having threads 116 on one end.

The fixation nail 100 may be formed of any material suitable forplacement into a bone without harmful effects on the patient. Examplesof suitable materials include, but are not limited to titanium and itsalloys, tantalum and its alloys, nickel-cadmium and its alloys, steeland its alloys, plastics, absorbable materials, resorbable materials,polyamino acids, polylactide, polyglycolide, hydroxylapatite, andtricalciumphosphate. Other materials useful for bone nail constructionwill be known to those skilled in the art, and are to be included withinthe scope of the present invention.

The bores 118 may be defined in the walls of the shaft 108 along thelength of the fixation nail 100. The bores 118 provide apertures throughwhich second fixation devices, shown as fixation screws 130 and 140, maybe passed in order to affix the fixation nail 100 to the bone 102.According to an exemplary embodiment, the bores 118 are oriented suchthat the fixation screws 130 or 140 pass through the fixation nail 100substantially perpendicular to the longitudinal axis of the fixationnail 100. In another embodiment, the bores 118 are oriented such thatthe fixation screws 130 or 140 pass through the fixation nail 100 atacute or obtuse angles with respect to the longitudinal axis of thefixation nail 100. The dimensions of a fixation screw that passesthrough the cannulated portion of a fixation nail are desirably selectedsuch that the screw does not substantially impede the passage of asubstance to be delivered to the bone.

In one embodiment, the screws 130 and 140 include an elongated shaftthat is sized to pass through the bore 118. In some instances, thefixation screws 130 and 140 may be cannulated and include a longitudinalbore that allows for the passage of the substance. In one embodiment,the screws 130 and 140 include external threads along at least a portionof the exterior of the shaft that pass through the bore 118 and areconfigured to engage the bone tissue. The screws 130 and 140 may be anysuitable threaded fastener known in the art, including cancellousscrews, cortical screws, and machine screws. In other embodiments, thefixation nail 100 may be affixed to the bone 102 with a non-threadedfixation device, such as tacks, pins, nails and the like.

The screws 130 and 140 may be formed of any material suitable forplacement into a bone without harmful effects on the patient. Examplesof suitable materials include, but are not limited to titanium and itsalloys, tantalum and its alloys, nickel-cadmium and its alloys, steeland its alloys, plastics, absorbable materials, resorbable materials,polyamino acids, polylactide, polyglycolide, hydroxylapatite, andtricalciumphosphate. Other materials useful for bone screw constructionare known to those skilled in the art, and are to be included within thescope of this disclosure.

Referring now to FIG. 3, passages 120, aligned with each of the bores118, are formed in the bone 102 with a drill 200 having a drill bit 202.The passages 120 are configured to receive the screws 130 and 140. Thedrill 200 may be a positioned relative to the fixation nail 100 with anexternal structure (e.g., bracket, arm, fixture, etc.) to maintain thealignment between the passage 120 and the respective bore 118. The drill200 is activated to rotate the drill bit 202, which is advanced into thebone 102. As the drill bit 202 is advanced into the bone 102, it removesbone tissue to form the passage 120. The drill bit 202 passes throughthe bore 118 and forms a passage 120 with a first portion 122 on oneside of the fixation nail 100 and a second portion 124 on the oppositeside of the fixation nail 100. Once the passage 120 is formed, the drillbit 202 is withdrawn from the bone 102. The screw 130 or 140 may then beadvanced through the passage 120 and the bore 118 to engage the bone 102and secure the fixation nail 100 to the bone 102.

Referring now to FIG. 4, the drill bit 202 is shown according to anexemplary embodiment. The drill bit 202 includes a drill body 204(distal portion) with cutting edges 208 that are configured to cut andremove material from the passage 120 and a shank portion 206 (proximalportion) that is engaged by a drive mechanism of the drill 200. Thedrill bit 202 is formed from a material suitable for placement into abone without harmful effects on the patient. According to an exemplaryembodiment, at least a portion of the drill bit 202 including thecutting edges 208 is formed of a material with a hardness that is lessthan the hardness of the material used to form the fixation nail 100.Because the hardness of the portion of the drill bit 202 including thecutting edges 208 is less than the hardness of the fixation nail 100,the drill bit 202 will not damage the fixation nail 100 if itinadvertently contacts the fixation nail 100 while forming the passage120 (e.g., contacting the portions of the shaft 108 surrounding thebores 118). The drill bit 202 may be configured to be reusable andsterilized after each use or the drill bit 202 may be configured to bedisposable and be replaced after use.

The material(s) chosen to form the drill bit 202 may vary depending onthe material of the components of the fixation system, such as thefixation nail 100. According to an exemplary embodiment, the fixationnail 100 is formed from a austenitic stainless steel (e.g., 316LVMstainless steel), which has a hardness of approximately 160 HB. At leasta portion of the drill bit 202 for use with such a fixation nail maytherefore be formed of a material with a hardness that is less thanapproximately 160 HB, such that it does not damage the fixation nail,but greater than the hardness of the bone such that it is able to removebone tissue to form the passage 120. According to another exemplaryembodiment, the fixation nail 100 may be formed from a harder material,such as a titanium alloy (Ti-6A1-4V), which has a hardness ofapproximately 334 HB. At least a portion of the drill bit 202 for usewith such a fixation nail may be formed of a material with a hardnessthat is less than approximately 334 HB, such that it does not damage thefixation nail, but greater than the hardness of the bone such that it isable remove bone tissue to form the passage 120.

According to an exemplary embodiment, the drill bit 202 is formed from apolymer with a hardness that is greater than bone but less than thehardness of the fixation nail 100. For example, the drill bit 202 or aportion of the drill bit 202 may be formed from polyetheretherketone(PEEK), polysulfone (PSU), polyphenylsulfone (PPSU), polyether imide(PEI), or any other suitable polymer or polymer composite material.According to another exemplary embodiment, the drill bit may be formedfrom a metal or metal alloy with a hardness that is greater than bonebut less than the hardness of the fixation nail 100.

Referring now to FIG. 5, according to another exemplary embodiment, adrill bit 302 may be formed from multiple materials. The drill bit 302includes an inner portion or core 304 formed from a first material andan outer portion or outer layer 306 formed from a second material thatis positioned over the core 304. For example, the core 304 may be formedof a stainless steel alloy (e.g., 316LVM stainless steel), while theouter layer 306 may be polyetheretherketone. The core 304 may be formedof a material that is equal in hardness or harder than the fixationnail. The outer layer 306 may extend over a portion of a drill body 308(e.g., the forward portion of the drill body 308 proximate a cuttingedge 310), over the entire drill body 308, or over the drill body 308and all or a portion of a shank 312. In this way, the material formingthe core 304 may be chosen to achieve a desired structural performance(e.g., stiffness, torsional strength, etc.) of the drill bit 302, whilethe material forming the outer layer 306 may be chosen to avoid damagingthe fixation nail while still being capable of cutting through the bone.

Referring now to FIG. 6, according to another exemplary embodiment, adrill bit 402 may be formed from multiple materials. The drill bit 402includes a tip 404 formed from a first material and a main body 406formed from a second material, with the tip 404 forward of the main body406. For example, the tip 404 may be formed of a relatively hardmaterial such as a stainless steel alloy (e.g., 416LVM stainless steel)or a titanium alloy, while the main body 406 may be a softer material,such as polyetheretherketone. The tip 404 may be formed of a materialthat is harder than the fixation nail. The tip 404 may include a portionof a cutting edge 410 (e.g., the interior portion of the cutting edge410) or may include the entire cutting edge 410. In this way, thematerial forming the tip 404 may be chosen to achieve a desiredpenetration of the bone, while the material forming the portions of thedrill bit 402 that are most likely to contact the portions of thefixation nail (e.g., the main body 406 and the outer portion of thecutting edges 410) may be chosen to avoid damaging the fixation nail. Insome embodiments, a drill bit may include both a core and a tip that isformed from a relatively hard material. The core and the tip may beformed from a continuous body or may be separate bodies which are eachcoupled to a softer material.

Referring now to FIG. 7, according to another exemplary embodiment, adrill bit 502 may be cannulated. The drill bit 502 includes a first end504 and a second end 506 with a drill bit cannulation 508 extendingbetween the ends 504 and 506 and forming openings at each end of thedrill bit 502. The drill bit cannulation 508 provides a passage throughwhich an installation device such as a guide wire may pass. After afixation nail, such as fixation nail 100 has been positioned in a bone,a guide wire may be inserted into the bone and through a bore, such asthe bore 118 in the fixation nail 100. The distal end of the guide wiremay then be inserted into the drill bit cannulation 508 to align thedrill bit 502 with the bore 118 in the fixation nail 100. After forminga passage in the bone, the drill bit 502 may then be removed from theguide wire and the guide wire may be used to facilitate the insertion ofa fixation device in the passage. As illustrated in FIG. 7 according toone embodiment, the drill bit cannulation 508 may be formed in a core510 formed of a first material. An outer layer 512 may be positionedover the core 510 and formed of a second material, similar to the drillbit 302, illustrated in FIG. 5. In other embodiments, the cannulation508 may be provided in a drill bit formed of a single material, similarto the drill bit 202 illustrated in FIG. 4.

Referring now to FIG. 8, a method 600 of preparing a bone to receive afixation screw through a fixation device positioned in a bone is shownaccording to an exemplary embodiment. The fixation device includes ashaft and at least one bore through the shaft. A guide wire may beoptionally placed through the bone and through the bore (step 602). Adrill is provided, the drill having a drill bit sized and configured topass through a bore in the fixation device (step 604). At least an outerportion of the drill bit has a hardness that is less than the hardnessof the fixation device. If a guide wire is used, the drill bit is passedover the guide wire. The drill is used to drill into the bone, advancingthe drill bit into the bone and through the bore (step 606). Once thedrill has formed a passage in the bone aligned with the bore, a fixationscrew may be fixed in the bore of the fixation device and into the boneto secure placement of the fixation device in the bone (step 608). Thedrill bit may be removed from the drill after use to be replaced by anew drill bit for subsequent procedures (step 610).

According to an exemplary embodiment, various components of a fixationsystem may be packaged together as a kit. For example, a fixation systemkit may include a fixation nail formed of a first material and one ormore drill bits sized to be received in bores in the fixation nail. Thedrill bits are least partially formed from a second materialspecifically selected to have a hardness that is greater than bone butless than the hardness of the fixation nail. By providing the fixationnail and drill bits in a kit, a user does not need to use a preexistingdrill bit, which may be as hard or harder than the fixation nail and maypotentially damage the fixation nail. The drill bits may be disposableto prevent the future use of a drill bit with a fixation nail that isnot as hard as the drill bit. The fixation system kit may furtherinclude other devices used to install the fixation nail, such asfixation screws, guide wires, location and aiming jigs and templates,measuring devices, etc.

Other devices may also benefit from being at least partially formed froma material specifically selected to have a hardness that is greater thanbone, but less than the hardness of other surgical devices. For example,another rotary tool, such as a reamer used to enlarge and smooth apassage (e.g., the passage 120 formed by the drill bit 202), may have atleast an outer portion that is formed of a material such aspolyetheretherketone (PEEK) that will not damage the fixation nail 100formed of a relatively hard material such as stainless steel or atitanium alloy.

While the drill bits 202, 302, 402, and 502 have been described for usewith the fixation nail 100, similarly constructed drill bits and othertools may be utilized to advantageously reduce damage to otherorthopedic devices in areas (e.g., high stress areas) where they may beinadvertently contacted and damaged by tools or other orthopedicdevices. For example, a drill bit for use with a cervical plate may beat least partially formed from a material specifically selected to havea hardness that is greater than the bone being drilled into, but lessthan the hardness of the plate.

Further modifications and alternative embodiments of various aspects ofthe invention will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only. The construction and arrangements of the bone screwsand inserts, as shown in the various exemplary embodiments, areillustrative only. Although only a few embodiments have been describedin detail in this disclosure, many modifications are possible (e.g.,variations in sizes, dimensions, structures, shapes and proportions ofthe various elements, values of parameters, mounting arrangements, useof materials, colors, orientations, etc.) without materially departingfrom the novel teachings and advantages of the subject matter describedherein. Some elements shown as integrally formed may be constructed ofmultiple parts or elements, the position of elements may be reversed orotherwise varied, and the nature or number of discrete elements orpositions may be altered or varied. The order or sequence of anyprocess, or method steps may be varied or re-sequenced according toalternative embodiments. Other substitutions, modifications, changes andomissions may also be made in the design, operating conditions andarrangement of the various exemplary embodiments without departing fromthe scope of the present disclosure.

What is claimed is:
 1. A method of preparing a bone to receive asecondary fixation element through a fixation device, comprising:providing a drill having a drill bit sized and configured to passthrough a bore in a fixation device positioned in the bone; and drillinga passage in the bone, wherein the passage extends through the bore;wherein at least a distal portion of the drill bit passes through thebore in the drilling step; and wherein at least an outer portion of thedistal portion of the drill bit has a hardness that is less than ahardness of the fixation device.
 2. The method of claim 1, wherein thedrill bit is cannulated for receiving a guide wire.
 3. The method ofclaim 2, further comprising placing a guide wire through the bone andpassing the drill bit over the guide wire to prepare the bone to receivethe secondary fixation element.
 4. The method of claim 1, furthercomprising removing the drill bit after use to be replaced by a newdrill bit for a subsequent procedure.
 5. The method of claim 1, whereinthe distal portion of the drill has a hardness that is greater than thehardness of the bone being drilled therein.
 6. The method of claim 1,wherein the drill bit comprises an outer layer formed of a secondmaterial positioned over an inner core formed of a harder material. 7.The method of claim 6, wherein the inner core of the drill bit is madeof stainless steel.
 8. The method of claim 7, wherein the secondmaterial is a plastic material.
 9. The method of claim 8, wherein thesecond material is polyetheretherketone.
 10. The method of claim 9,wherein the hardness of the second material is greater than the hardnessof the bone and less than a Brinell hardness of 160 HB.
 11. The methodof claim 1, further comprising inserting the fixation device into thebone, the fixation device comprising a shaft and at least one boretherethrough for receiving a fixation screw.
 12. The method of claim 11,further comprising fixing a fixation screw into the bore of the fixationdevice and into the bone to thereby secure placement of the fixationdevice in the bone.
 13. A bone fixation system, comprising: a fixationdevice configured to be positioned at a target area of bone comprisingtwo ends connected by a shaft and further comprising a bore formedthrough the shaft configured to receive a fixation screw; a drill bitsized and configured to pass through the bore to prepare the surroundingbone to receive a second fixation device; wherein at least a distalportion of the drill bit is configured to pass through the bore; whereinthe fixation device is made of a first material and wherein the distalportion of the drill bit comprises at least an outer portion made of asecond material; and wherein the second material of the drill bit has ahardness that is less than the hardness of the first material of thefixation device.
 14. The system of claim 13, wherein the second materialhas a hardness that is greater than the hardness of the portion of thebone being drilled.
 15. The system of claim 13, wherein the drill bit iscannulated for receiving a guide wire.
 16. The system of claim 13,wherein the drill bit comprises an outer sheath formed of the secondmaterial positioned over an inner core made of a harder material. 17.The system of claim 13, wherein the second material ispolyetheretherketone.
 18. The system of claim 13, where in the drill bitis disposable after drilling.
 19. The system of claim 13, wherein theshaft of the fixation device is cannulated along at least a portion ofits length, and wherein the fixation device comprises at least onefenestration along the cannulated portion of the fixation device shaft.20. The system of claim 19, wherein the fixation device is adapted toreceive an insert portion in the fixation device cannulation.
 21. Thesystem of claim 13, wherein the hardness of the second material isgreater than the hardness of the bone and less than a Brinell hardnessof 160 HB.
 22. The system of claim 13, further comprising a fixationscrew configured to be received in the bore.
 23. A drill bit forpreparing a hole in a bone, comprising: a drill bit shaft having adistal portion sized and configured to be received through a bore in afixation device, wherein the distal portion has a hardness greater thanthe hardness of the bone and less than a Brinell hardness of 160 HB.